1. Field of the invention
The present invention generally relates to vapor recovery apparatus for use in fuel dispenser applications, and, more particularly, to method and apparatus for detecting hydrocarbon emissions discharged during refueling activity using a fiber-optic sensor and for regulating the vapor pump based on the sensed hydrocarbon concentration.
2. Description of the related art
As gasoline or other fuel is dispensed into an automobile or other motor vehicle from a fuel delivery system, the incoming fuel displaces volatilized fuel vapors and forces their discharge from the containment tank. These vapors must be captured or otherwise collected to prevent their escape and contamination of the surrounding environment. Vacuum-assisted stage II vapor recovery systems serve to recover hydrocarbon vapors displaced from vehicle fuel tanks during fuel dispensing operations. The released vapors are collected by using a vapor pump to draw vapors into the vapor recovery system for subsequent storage, recycling or destruction. The rate at which vapor is collected is controlled by varying the speed of the vapor pump. For maximum performance and efficiency of the vapor recovery system, the speed of the vapor pump must be adequately controlled so that vapor is collected at a rate that corresponds as closely as possible to the instantaneous rate of effluent vapor discharge that is developed during a refueling operation, while minimizing the retrieval of oxygen.
The challenge encountered by all such vacuum-assisted vapor recovery systems is finding a suitable vapor monitoring system capable of dynamically sensing the presence of hydrocarbon components and generating a signal that accurately measures the detected hydrocarbon. One limitation experienced by conventional detection apparatus involves an inability to sense hydrocarbon in both its vapor state and liquid state. This deficiency is most pronounced when the refueling operation occurs during temperature and pressure conditions favorable to the condensation of gaseous hydrocarbon. The absence of any capability to adequately remove the hydrocarbon condensate leads to false readings and an overall corruption of the sensing measurement data, resulting in an unreliable control mechanism for regulating the vapor pump.
It is also critical to proper functioning of the vapor recovery system that the vapor sensing element be highly sensitive to the presence of hydrocarbon. Otherwise, if low levels of hydrocarbon concentration fall below a threshold point at which the sensing element becomes incapable of registering the presence of hydrocarbon, the vapor pump will be directed to continue in operation at its current speed corresponding to the registration of a prior level of hydrocarbon detection that is no longer valid. This undetected condition may lead to excessive collection of oxygen components due to the mismatch between the vapor pump operating speed and the actual but undetected hydrocarbon concentration.